The present invention relates to battery parts made of polyolefin resin. More particularly, the present invention relates to battery parts comprising polyolefin resin moldings bonded together, with an adhesive processing and a process thereof. The parts produced according to the present invention is particularly useful for lithium batteries.
Since polyolefin resins are excellent in heat and chemical resistance, the polyolefin resins have been widely utilized for preservation containers of chemical and medicinal substances, etc., and have recently been used for the containers of various types of battery such as lithium batteries, alkaline batteries and lead batteries.
In manufacturing battery parts by bonding the polyolefin resin moldings, since there is no functional group in the resin constituting the surface to be bonded of the polyolefin resin moldings, it is required to (1) fusion-bond the moldings or (2) bond them with adhesive after surface treatment with plasma, chromic acid or a primer.
The fusion-bonding, however, has some serious disadvantages such as poor dimensional precision of the produced container, need of use of high temperature for bonding work, and great difficulties in conducting high-temperature fusion-bonding of the moldings such as cover of a battery containing an organic solvent-type electrolysis solution.
On the other hand, in case of plasma surface treatment, since a high-vacuum apparatus is required and in case of the surface treatment with a chemical substance such as chromic acid, there are problems of treatment of a strong acid and disposal of the waste chemicals. Also, in case of the surface treatment using a primer, there is a problem of desiccation since the primer itself is a solvent.
Further, when the surface-treated moldings are bonded together with an epoxy or acrylic adhesive, the bonded portions may be affected and reduced in bonding strength by the acid electrolysis solution in the case of lead batteries, by the alkaline electrolysis solution in the case of alkaline batteries, and by the electrolysis solution comprising organic solvents, in the case of lithium and other similar types of batteries. Also, since those adhesives are hard, the bonded portions, when being subject to an external force such as vibrations, may be cracked to cause leakage of the electrolysis solution. Particularly in the case of lithium batteries which need to be strictly protected against moisture, degradation of the bonded portions is fatal.
Injection molding is conducted for manufacturing polyolefin resin-made battery containers, but this method has difficulties in working of complicate configurations and also involves problems on cost and environmental protection.
As a result of the present inventors' earnest studies to solve the above problems, it has been found that by using a reactive hot-melt adhesive after conducting surface treatment of the moldings with a mixture comprising fluorine-containing gas, preferably a mixture comprising fluorine gas and oxygen gas or a mixture comprising fluorine gas, sulfur dioxide gas and oxygen gas, it is possible to bond the polyolefin resin moldings to each other strongly with high dimensional precision. The present invention has been attained on the basis of the above finding.